65 terms

Exercise Physiology- Ch. 5 (Energy Expenditure and Fatigue)

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direct calorimetry
"measuring heat"; 60% of energy liberated during metabolism of glucose and fats is converted to heat, so one way to gauge the rate and quantity of energy production is to measure the body's heat production
pros of direct calorimetry
accurate over time; good for resting metabolic measurements
cons of direct calorimetry
expensive, slow, exercise equipment adds extra heat, sweat creates errors in measurements, not practical or accurate for exercise
calorie (cal)
basic unit of heat
calorimeter
insulated, airtight chamber with walls containing tubing with circulating water; heat produced by the body radiates to the walls and warms the water; water temp and temp changes in the air vary with the heat the body generates so one's metabolism can be calculated from the resulting values
indirect calorimetry
energy expenditure can be determined by measuring the respiratory exchange of O2 and CO2; heat production is not measured directly; technique limited to steady-state aerobic activities lasting a few minutes or longer; older methods of analysis accurate but slow, newer methods faster but expensive
indirect calorimetry limitations
CO2 production may not equal CO2 exhalation; RER inaccurate for protein oxidation; RER near 1.0 may be inaccurate when lactate buildup exceeds CO2 exhalation; gluconeogenesis produces RER <0.70
VO2
actual volume of oxygen consumed; rate of O2 consumption;
volume of inspired O2 - volume of expired O2
VCO2
volume of CO2 produced; rate of CO2 production;
volume of expired CO2 - volume of inspired CO2
inspired air makeup
3 gases: oxygen (20.93%), carbon dioxide (0.04%), and nitrogen (79.03%); inspired O2 per minute may not equal expired CO2 per minute; inspired N2 per minute equals expired N2 per minute
haldane transformation
allows V of inspired air (unknown) to be directly calculated from V of expired air (known); based on constancy of N2 volumes;
VI = (VE x FEN2)/FIN2
VO2 = (VE) x {[1-(FEO2 + FECO2) x (0.265)] − (FEO2)}
respiratory exchange ratio
ratio between rates of CO2 production and O2 usage; RER=VCO2/VO2; O2 usage during metabolism depends on type of fuel being oxidized (more carbon atoms in molecule=more O2 needed; glucose<palmitic acid); as % of Kcal from carbs increase, RER increases; as % of Kcal from fats increase, RER decreases
RER for 1 molecule glucose
6 O2 + C6H12O6 -> 6 CO2 + 6 H2O + 32 ATP
RER= VCO2/VO2 = 6 CO2/6 O2 = 1.0
RER for 1 molecule palmitic acid
23 O2 + C6H32O2->16 CO2 + 16 H2O + 129 ATP
RER= VCO2/VO2 = 16 CO2/23 O2 = 0.70
isotopes
elements with an atypical atomic weight; can be radioactive or nonradioactive
Carbon-13
constitutes about 1% of the carbon in nature; nonradioactive; frequently used for studying energy metabolism
H-2 (deuerium)
another common isotope for studying energy metabolism
measuring anaerobic capacity
no clear method; imperfect but accepted methods: maximal accumulated O2 deficit, wingate anaerobic test, critical power test
isotopic measurements of energy metabolism
isotopes can be selectively followed in the body by infusing isotopes into an individual and following their distribution and movement; turnover is relatively slow, so energy metabolism must be measured for several weeks; not suited for measurements of acute exercise metabolism; 98% accurate and low risk
metabolic rate
rate at which the body uses energy; based on whole body O2 consumption and corresponding caloric equivalent; at rest, RER ~0.80, VO2 ~0.3 L/min, metabolic rate ~2,000 kcal/day
basal metabolic rate (BMR)
standardized measure of energy expenditure at rest; rate of energy expenditure for an individual at rest in a supine position, measured in a thermoneutral environoment immediately after at least 8 h of sleep and 12 h of fasting; minimum amount of energy required to carry on essential physiological functions; directly related to individual's fat free mass
factors affecting BMR/RMR
gender: BMR is typically lower for women
age: BMR decreases with age
body temp: BMR increases with increasing temp
stress level: stress increases BMR
hormones: thyroxine and epinephrine both increase BMR
resting metabolic rate (RMR)
similar to BMR but does not require stringent standardized conditions of a true BMR; BMR and RMR values are typically within 5%-10% of each other (BMR slightly lower); ~1,200 to 2,400 kcal/day
daily energy expenditure
includes normal daily activities; normal= 1,800 to 3,000 kcal/day
sedentary person: 8% thermic effect of feeding, 17% energy expenditure of physical activity, 75% resting energy expenditure
physically active person: 8% thermic effect of feeding, 32% energy expenditure of physical activity, 60% resting energy expenditure
energy expenditure during submaximal aerobic exercise
metabolic rate increases with exercise intensity; slow component of O2 uptake kinetics (at higher power outputs, VO2 continues to increase, more type II fiber recruitment); VO2 drift
VO2 drift
upward drift observed even at low power outputs; possibly due to ventilatory, hormone changes?
maximal oxygen uptake (VO2max)
the maximal limit of ability to increase VO2; best single measurement of cardiorespiratory endurance/aerobic fitness; not best predictor of endurance performace; expressed in L/min for non-weight bearing activities; typically expressed relative to body weight to get a more accurate comparison of cardioresiratory endurance capacity of difference sized individuals during weight bearing events mL O2 x kg^-1 x min^-1
peak oxygen uptake (VO2peak)
subject reaches volitional fatigue before a plateau occurs in the VO2 response; the highest oxygen uptake achieved
VO2 max after chronic training
increases for 8 to 12 weeks and then plateaus despite continued higher-intensity exercise
normal VO2max values
untrained young female= 38-42 ml x kg^-1 x min ^-1
untrained young male= 44-50 ml x kg^-1 x min^-1
VO2 max after years of inactivity
after the age of 25-30, VO2max decreases at a rate of about 1% per year due to biological aging and sedentary lifestyle
VO2 max gender difference
different body composition (women generally have less fat free mass and more fat mass) and blood hemoglobin content (lower in women=lower oxygen carrying capacity)
energy expenditure during maximal anaerobic exercise
no activity 100% aerobic or anaerobic; estimates of anaerobic effort involve excess postexercise O2 consumption and lactate threshold
oxygen deficit
oxygen needs and oxygen supply differ during the transition from rest to exercise; calculated as the difference between the oxygen required for a given exercise intensity (steady state) and the actual oxygen consumption
excess posteexercise oxygen consumption (EPOC)
excess oxygen consumption which exceeds that required at rest; volume of oxygen consumed during the minutes immediately after exercise ceases that is above that normally consumed at rest
alactacid EPOC (fast component)
portion of O2 required to synthesize and restore muscle phosphagen stores (ATP and PC)
lactacid EPOC (slow component)
portion of O2 required to remove lactic actid from the muscle cells and blood
lactate threshold
the point at which blood lactate begins to substantially accumulate above resting concentrations during exercise of increasing intensity; good indicator of an athletes potential for endurance exercise; determined by the production of lactate as well as the clearance of lactate from the blood by the liver; best defined as the point in time during exercise of increasing intensity when the rate of lactate production exceeds the rate of lactate clearance
typical lactate threshold values
untrained: occurs at 50-60% of VO2 max
trained: 70-80% of VO2 max
anaerobic threshold
the sudden increase in blood lactate with increasing effort
characteristics of successful athletes in aerobic endurance events
high VO2 max, high lactate threshold, high economy of effort, high percentage of type I muscle fibers
energy cost of various activities
varies with type and intensity of activity; calculated from VO2 and expressed in kcal/min; values ignore anaerobic aspects and EPOC
total daily caloric expenditure depends on:
physical activity, age, sex, body size, body weight, and body composition
economy of effort
as athletes become more skilled, they use less energy for a given pace; independent of VO2 max; body learns energy economy with practice; economy increases with distance of race; practice yields better economy of movement (form); varies with type of exercise
fatigue
decrements in muscular performance with continued effort accompanied by general sensations of tiredness; inability to maintain the required power output to continue muscular work at given intensity; reversible by rest
underlying causes of fatigue
decreased rate of energy delivery (ATP-PCr, anaerobic glycolysis, and oxidative metabolism); accumulation of metabolic by-products such as lactate and H+; failure of the muscle fiber's contractile mechanism; alterations in neural control of muscle contraction
peripheral fatigue
alterations at the motor unit level
central fatigue
changes in the brain or central nervous system
PCr depletion
during repeated maximal contractions, fatigue coincides with PCr depletion; as PCr is depleted, the ability to quickly replace the spent ATP is hindered; pacing helps to defer
glycogen depletion
glycogen reserves are limited and are depleted quickly; correlation between glycogen depletion and fatigue during prolonged exercise (not a direct relation); unrelated to rate of glycogen depletion; dpeletes more quickly at high intensity and during first few minutes of exercise; type I fibers depleted more quickly; depletion can occur in different muscle groups depending on exercise; after blood glucose concentrations decrease, the muscles must rely more heavily on glycogen reserves, accelerating depletion
inorganic phosphate
increases during intense short term exercise as PCr and ATP are broken down; may be the largest contributor to fatigue in this type of exercise; impairs contractile function of myofibrils and can reduce Ca2+ release from SR
heat and muscle temp and fatigue
exercise in the heat can increase rate of carbohydrate utilization and hasten glycogen depletion; high muscle temps impair both skeletal muscle function and muscle metabolism; 11 degrees C: time to exhaustion longest, 31 degrees C: time to exhaustion shortest
lactic acid, hydrogen ions, and fatigue
when lactic acid is not cleared, is dissociates, converting to lactate and causing an accumulation of hydrogen ions; H+ accumulation causes muscle acidosis (decreased pH) slowing rate of glycolysis and ATP production and displacing calcium with the fiber, interfering with the coupling of the actin-myosin cross bridges; buffers help muscle pH but not enough; takes 30-35 min of recovery to reestablish preexercise muscle pH after exhaustive sprint
benefits of lactic acid
serves as source of fuel; directly oxidized by type I fiber mitochondria, shuttled from type II fibers to type I for oxidation, converted to glucose via gluconeogenesis (liver)
fatigue at neuromuscular junction
prevents nerve impulse transmission to the muscle fiber membrane; possible causes: decreased ACh sythesis/release, altered ACh breakdown in synapse, increase in mmuscle fibeer stimulus threshold, altered muscle resting membrane potential; fatigue may inhibit Ca2+ release from SR
central governor theory
processes occur in the brain that regulate power output by the muscle to maintain homeostasis and prevent unsafe levels of exertion that may damage tissues or cause catastrophic events; limits exercise by decreasing the recruitment of muscle fibers, in turn causing fatigue
acute muscle soreness
pain felt during and immediately after exercise; classified as a muscle strain and perceived as muscle stiffness, aching, or tenderness; caused by accumulation of end products of exercise and from tissue edema (cause of acute muscle swelling)
delayed-onset muscle soreness (DOMS)
soreness felt a day or two after a heavy bout of exercise; can vary from slight muscle stiffness to severe, debilitating pain that restricts movement; eccentric muscle action is the primary initiator
structural damage after intense exercise
enzyme concentrations in the blood indicate various degrees of muscle tissue breakdown; damage is responsible in part for localized muscle pain, tenderness, and swelling associated with DOMS
muscle inflammation after intense exercise
soreness results from inflammatory reactions in the muscle
sequence of events in DOMS
1. high tension in muscle leads to structural damage to muscle or cell membrane
2. membrane damage disturbs Ca2+ homeostasis in injured fiber
3. after a few hours, circulating neutrophils increase
4. products of macrophage activity, intracellular contents accumulate
5. fluid and electrolytes shift into the area creating edema
loss of strength from DOMS is the result of:
1. the physical disruption of the muscle
2. failure within the excitation-contraction coupling process
3. loss of contractile protein
minimizing DOMS
minimize eccentric work early in training; start training at very low intensity and progress slowly through the first few weeks; initiate the training program with high-intensity, exhaustive training bout (muscle soreness would be great for the first few days, but subsequent training bouts would cause considerable less muscle soreness)
exercise induced muscle cramps (EAMCs)
painful, spasmodic, involuntary contractions of skeletal muscles that occur during or immediately after exercise; fatigue causes altered neuromuscular control and results in the excitation of muscle spindle and inhibition of Golgi tendon organ; relieved by stretching
heat cramps
associated with large sweat and electrolyte losses, especially sodium and chloride; treatment is high-sodium solution, ice, and massage